This invention relates in general to coded data conversion and more particularly, to analog to digital conversion.
For vulnerability tests where the shock loading is difficult to predict and is not always repeatable, the data acquisition procedure used for digitizing analog signals is to set the system gain low enough to allow a signal 10 times larger than expected to be recorded without clipping. Preventing clipping of the digitized signal is important since any information about peak signal is lost and the shock response spectral analysis is distorted. However, when this is done, an expected signal uses only 10% of the digitizer range, resulting in a lower signal-to-noise ratio. A worse than expected signal ({fraction (1/100)}th of full scale) uses only 1% of the digitizer range and it has a poor signal-to-noise ratio.
It is therefore an object of this invention to optimize the digitizing of analog signals having a large dynamic range variation.
This and other objects of the invention are achieved by an apparatus and a method for digitizing an analog signal and optimizing the dynamic range of the digitized signal. An analog input signal is fed to each of a pair of amplifiers with different gains and then to respective analog-to-digital converters. The digital signal from the analog-to-digital converter preceded by the amplifier of higher gain is selected and stored in a digital memory when it is not clipped. When clipping occurs, the digital signal from the analog-to-digital converter preceded by the amplifier of lower gain is selected and stored in the digital memory. Once the memory is filled, an adaptive formatting program selects the most appropriate parts of the memory words to achieve maximum resolution and dynamic range in an output word size. The adaptive reformatting provides improved dynamic range over currently available single analog-to-digital converter circuits.
Although designed to optimize recording of transients which typically have a high dynamic range, this technique is also applicable to testing where unexpected results are not anticipated since the low gain analog-to-digital converter provides insurance that if anything goes wrong a higher dynamic range signal will be recorded.
Additional advantages and features will become more apparent as the subject invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: